Schedule of Option Activity and Changes (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Outstanding at December 31, 2011	1,133,147
Options, Granted	115,340
Options, Exercised	(223,044)
Options, Cancelled	(1,278)
Options, Outstanding at June 30, 2012	1,024,165
Options, Exercisable at June 30, 2012	648,698
Weighted Average Exercise Price, Outstanding at December 31, 2011	$ 23.26
Weighted Average Exercise Price, Granted	$ 60.09
Weighted Average Exercise Price, Exercised	$ 20.21
Weighted Average Exercise Price, Cancelled	$ 43.92
Weighted Average Exercise Price, Outstanding at June 30, 2012	$ 28.05
Weighted Average Exercise Price, Exercisable at June 30, 2012	$ 20.92
Weighted Average Remaining Term (Years), Outstanding at June 30, 2012	6 years 6 months
Weighted Average Remaining Term (Years), Exercisable at June 30, 2012	5 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding at June 30, 2012	$ 25,693
Aggregate Intrinsic Value, Exercisable at June 30, 2012	$ 20,331